/Engine/Plugins/Online/OnlineServices/Source/OnlineServicesCommon/Public/Online/SessionsCommon.h
struct FSessionEvents
TOnlineEventCal...
OnSessionInviteReceived
TOnlineEventCal...
OnSessionJoined
TOnlineEventCal...
OnSessionLeft
TOnlineEventCal...
OnSessionUpdated
TOnlineEventCal...
OnUISessionJoinRequested